JPS62133093A - Continuous production of m-hydroxybenzyl alcohol - Google Patents

Abstract

PURPOSE:To continuously produce m-hydroxybenzyl alcohol in a high yield by continuously feeding m-hydroxybenzoic acid and an acidic aqueous soln. as starting materials, allowing m-hydroxybenzyl alcohol to exist in the electrolytic soln. and carrying out electrolysis at a specified temp. CONSTITUTION:m-Hydroxybenzoic acid and 10-20wt% aqueous sulfuric acid soln. as starting materials are continuously fed to a multistage electrolytic cell. m-Hydroxybenzyl alcohol is allowed to exist in the electrolytic soln. in the electrolytic cell and continuous electrolysis is carried out at 20-70 deg.C, especially 30-60 deg.C reaction temp. to continuously produce m-hydroxybenzyl alcohol.

Description

[Detailed Description of the Invention] The present invention provides m-hydroxybenzyl alcohol (hereinafter referred to as m-hydroxybenzyl alcohol).
(abbreviated as HI30H).

mHBOH is a compound useful as an intermediate for pharmaceuticals or agricultural chemicals, but at present it has not been commercially supplied by an inexpensive manufacturing method.

Conventional methods for synthesizing mHBOH include fermentation using m-cresol as a raw material, sodium amalgam using m-hydroxybenzaldehyde as a raw material, NaBH,1, and LiAl.
There are reduction and hydrogenation reactions using H4, etc., but they have not been put to practical use because the yield is insufficient. Further, the hydrogenation reaction is a reaction at high temperature and high pressure, and there are various problems with industrial production methods.

Regarding the method using m-hydroxybenzoic acid (hereinafter abbreviated as mHBA) as a raw material, sodium amalgam and electrolytic reduction method have been proposed (Bericht U.
752 (1905)), but the yield was low and it could not be used as an industrial method.

Problems to be Solved by the Invention The present inventors have solved the following problems regarding the industrial production method of mHBOH:
After extensive research, we have previously discovered a method for obtaining high-yield, high-purity mHBOH@ by electrolytic reduction of mHBA (Japanese Patent Application No. 59-90887, Japanese Patent Application No. 59-96639). Although these electrolytic reactions are batch reactions, in order for the electrolytic reaction to proceed smoothly, it is necessary that the electrolytic solution is uniformly dissolved and that no damage is caused to the electrode surface.

mHBA has low solubility in water, and it has been difficult to increase the substrate concentration. It is desirable to have a substrate concentration of 10% or higher from the viewpoint of industrial production efficiency and economic efficiency, but in order to dissolve mHBA in an aqueous solvent to a concentration of 10% or higher, it is necessary to raise the temperature to 90°C or higher. , a method of increasing the concentration of mHBA by using a quaternary ammonium salt as a supporting electrolyte, and a method of increasing the solubility of mHBA by using a water-soluble organic solvent, 1f (B
A method of esterifying A to increase its water solubility is required.

It was also found that when electrolyzing mHBA in a solution state, it is necessary to make the solution acidic, and the present inventors have previously proposed these methods.

However, if a supporting electrolyte or an organic solvent is used during the reaction, separation from the organic solvent or supporting electrolyte becomes complicated to isolate mHBOH after electrolysis, which increases costs.
connected to. Furthermore, in the method of increasing solubility by raising the temperature, mHBA decomposes faster in an acidic aqueous solution as the temperature rises, which is not preferable.

FIG. 1 shows the respective mHBA solution temperatures when the sulfuric acid concentration in the mHBA sulfuric acid aqueous solution is 5% by weight and 25% by weight,
It is a relationship diagram with the mHBA thermal decomposition rate after 5 hours.

As can be seen from the figure, for example, 90%
When mHBA is dissolved at ℃, the decomposition proceeds at a rate of about 5 times per hour, which means that 4 to 5 hours is appropriate for the reaction in normal cases, but the total reaction time is 20°C. ~2596
It turns out that the decomposition of can not be ignored.

Furthermore, there was a problem with the heat resistance of the cation exchange membrane used in the diaphragm of the electrolytic cell, making electrolysis at high temperatures practically impossible.

In order to solve the problem, the present inventors conducted intensive studies on a method of dissolving the substrate in an acidic aqueous solution to a concentration of 10 or more and carrying out continuous electrolytic reduction, and completed the present invention.

Figure 2 shows the solubility curve of mHBA at each temperature using an aqueous solution of mHBOH added to 100 g of water as a parameter. Shows the weight of.

As can be seen from the figure, for example, by weighing 10 g of mHBOH, the solubility of mHBA becomes extremely high, and the mHBA decomposition rate is sufficiently solubility that it can be carried out even at a relatively low temperature of 70°C or lower. have

Thus, mHBA has low solubility in water, but mHBOH has high solubility in water, and mHBO
When H is dissolved, the solubility of mHBA increases.

Therefore, it is not necessary to add an organic solvent or a supporting electrolyte D11 to the electrolytic reduction reaction system, and the reaction can be carried out at a relatively low reaction temperature. For this purpose, it is necessary to always have mHBOH present in the electrolytic solution subjected to the electrolytic reduction reaction, but it is necessary to add mHBOH from the preparation stage to dissolve it, and then charge mHB A all at once. Depending on the method and the progress of the reaction, the mHBA consumed is added sequentially and cumulatively.
The present inventors previously proposed a semi-batch method in which the process is carried out while using L.

However, since this method is a semi-batch method, the amount of m I(B Of() in the tank fluctuates over time.
Therefore, it was necessary to vary the amount of mHBA to be dissolved each time.

As a result, not only the production efficiency was reduced, but also the reaction operation was complicated.

The inventors of the present invention conducted extensive research and found a manufacturing method with high production efficiency by continuously supplying an acid precipitate solution and mHBA into an electrolytic tank to perform electrolysis, and completed the present invention.

That is, in the present invention, when m-hydroxybenzoic acid is electrolytically reduced with an acidic aqueous solution, m-hydroxybenzoic acid as a raw material and the acidic aqueous solution are continuously added, m-hydroxybenzyl alcohol is made to exist in the electrolytic solution, and 20
This is a continuous method for producing hydroxybenzyl alcohol, characterized by carrying out electrolysis at ~70°C.

A preferred example of carrying out the method of the present invention will be described below.

The electrolytic cell is initially charged with an acidic aqueous solution.

Next, a certain amount of acidic aqueous solution and mHBA are continuously supplied, and electricity is applied to the anode and cathode in the electrolytic cell to perform continuous electrolysis.

On the other hand, the electrolytic solution is caused to flow out in a fixed amount from an overflow pipe provided on the side wall of the cathode cell, or from the cathode cell using a metering pump. In this case, it is preferable to provide a multistage electrolytic cell, and the effluent is continuously charged to the cathode cell.

At the start of electrolysis, the amount of 1HBOH dissolved in the electrode bath is small, and therefore the amount of mHBA added to the electrolyte needs to be reduced, but as time passes, mHBO
As the amount of H increases, the amount of mHBA dissolved also increases,
When it becomes constant, that is, in a steady state, a certain amount of mHBOH is always dissolved in the electrolytic cell, and the supplied mHBA
The amount of dissolved is also constant.

As a result, the concentration of the reaction substrate is always constant, continuous electrolysis is performed, and the electrolyte can be taken out.

The type of electrolytic cell is not particularly limited. m
It is sufficient if the solubility of HBA can be increased and the HBA can be subjected to electrolytic reduction.

In addition, in the present invention, the acidic aqueous solution is not particularly limited as long as it is an acidic substance that is inert to the electrolytic reaction at the cathode, but mineral acids are preferably used from the viewpoint of cost, especially from the viewpoint of material quality and yield. Sulfuric acid is a more preferred mineral acid.

An aqueous sulfuric acid solution having a concentration of 5 to 30% by weight, preferably 10 to 20% by weight is used. When the sulfuric acid concentration is low, such as 5 parts by weight or less, the decomposition rate of mHBA is small, but the reaction rate is slow, and at high concentrations, such as 30 parts by weight or more, the reaction rate is fast, but the decomposition rate of mHBA is slow. growing.

In the method of the present invention, the electrolytic reduction reaction temperature does not need to be maintained at 90°C or higher, but is 20 to 70°C, preferably 30°C.
Carry out at a temperature of ~60°C. In addition, electrolytic reduction with a substrate concentration of 10 parts or more is possible. In order to make mHBOH exist in the electrolyte, in the case of the present invention, the addition rate of mHBA is m
It can be determined by the consumption rate of the HBA, that is, the amount of current supplied. It is preferable to continuously add mHBA so that the concentration of mHBA in the electrolytic solution is maintained at 5 or less, so that the electrolytic reaction proceeds smoothly and the substrate concentration can be easily increased to 10 or more. However, if the concentration is too high, the viscosity will increase and have a negative effect on the electrode and ion exchange membrane, so the final reaction substrate concentration is preferably 30 parts or less, usually 10 to 15 parts, and it depends on the charging rate of the sulfuric acid aqueous solution. You can decide arbitrarily.

In addition, when the reaction temperature is 20°C or lower, mHBA in the electrolyte
is hardly dissolved, and for this purpose a large amount of mHBOH must be present, resulting in poor production efficiency. Also 70℃
In this case, the decomposition rate of mHBA is high, and in the present invention, mHBOH to be present in the electrolytic solution is determined according to the solubility of mHBA rather than the reaction temperature and acid concentration, and the concentration of the reaction substrate is taken into consideration. .

Furthermore, in the method of the present invention, materials having high hydrogen overvoltage, specifically zinc, lead, cadmium, and mercury, are used as the cathode material among the electrodes. The anode, on the other hand, is not particularly limited as long as it is made of a normal electrode material.

Although 771HBOH is produced even in an electrolytic cell without a diaphragm, the oxidation reaction also occurs at the anode, so the yield of mHBOH relative to mHBA decreases. For this reason, it is particularly preferable to isolate the anode chamber and the cathode chamber by a cation exchange membrane. As the material for the diaphragm, asbestos, ceramics, sintered glass, etc. can be used.

In the electrolytic reduction of the present invention, the current density is preferably 5 to
30A,/cm. Theoretically, it is a four-electron reduction,
Although the current flow is 4 F r/mode e, the current efficiency is 50 to 70%, so it takes 5 to 8 F to complete the reaction.
Fr/mole It is necessary to pass an amount of electricity.

The continuous method electrolyzer completely converts the raw material +nHBA into mHBO.
Although a large number of electrolytic cells are required for electrolytic reduction to H, if the presence of unreacted mHBA is allowed, the purpose can be achieved even with a single electrolytic reaction.

When electrolyzing using a large number of electrolytic cells, the raw material mHB
A, and the sulfuric acid aqueous solution should be charged in full in the first stage, or
It is optional whether to divide the charge into the second stage or later.

In this way, the method of the present invention performs the electrolytic reaction at 20 to 70°C, allows mHBOH to always exist at a constant concentration in the tank, and
Since HBA is dissolved to the maximum level in the tank at a predetermined temperature and electrolytic reduction is performed, it is possible to shorten the residence time per unit mHBOH compared to batch methods, etc.
Coupled with the fact that thermal decomposition of can be suppressed, the target product can be obtained in high yield.

Example Examples are shown below.

Example 1 Both electrode chambers had a capacity of 300 ml, and the cell was an H-type electrolytic cell separated by Selemion (CMV (a cation exchange membrane trade name of Asahi Glass Co., Ltd.)) as a diaphragm, and the cathode chamber had an overflow It has a side pipe so that the electrolyte can be continuously extracted when the volume exceeds 200 ml.

A 10% sulfuric acid aqueous solution is charged into both electrode chambers at a rate of 200 m/each.

A 50C11 lead plate was used as the cathode, and a 50CrI platinum plate was used as the anode. The electrolytic cell was maintained at 30°C, and a 10% sulfuric acid aqueous solution was supplied to the cathode chamber at a rate of 5o9/hour using a metering pump, and mHBA was supplied at a rate of 8.9/hour using a microfeeder, while 8.5A DC constant current electrolysis was carried out. was carried out for 15 hours. (
(0,317Fr/118) The catholyte was a homogeneous and transparent liquid. As a result of analyzing the catholytes 11o and 9 that flowed out in 2 hours using liquid chroma 1~graphie (HLC), it was found that mHBA
1.0%, mHBOHll, 9%.

mHBOH yield cz, os, current efficiency 666.

Example 2 The same electrolyzer as in Example 1 is used. The temperature was kept at 60''C, and 12A DC constant current electrolysis was performed for 15 hours while supplying 20% sulfuric acid aqueous solution at 50J/hour and 171HBA at 12g/hour to the cathode chamber. (0,448Fr/f Terama)
.

The catholyte was a homogeneous clear liquid. The result of HLC analysis of 115.9% of the catholyte that flowed out in 2 hours showed that mHBA
1. , 7%, mHBOH 16.9%.

mHBOH yield: 900, current efficiency: 69.9%
Example 3 The electrolytic cell has a lead plate (cathode) with an effective electrode area of 110×10 and a platinum plate (anode) of the same size as the diaphragm, Selemion CMV is used as the diaphragm, and the distance from the membrane to each electrode is 1
A filter press type (two sets of positive and private parts) electrolytic cell, which is CRN, was used. 10 in two 300 ml flasks
The relevant sulfuric acid aqueous solution was charged in 200 ml portions, and the electrolytic solution (sulfuric acid aqueous solution) was circulated to the anode chamber of the electrolytic cell using a pump. Yin h pH has a lateral canal and is 200+++1!
When the temperature exceeded this level, an overflow caused the liquid to flow into the cathode bath of a similar electrolyzer in the second stage. The raw material 10M sulfuric acid aqueous solution is charged to the first stage cathode tank at a rate of 50 J/hour, and the m
HBA was charged to the first and second stage cathode cells at 12 g/hour. Each type was kept at 60° C., and constant current electrolysis of 12 A was performed in each of the first-stage and second-stage electrolytic cells for 30 hours. (0,896 Fr/hour) The first and second stage cathode baths were uniform and transparent liquids. The HLC analysis results showed that the first stage mHBA was 2.0%, mHBOH was 16%,
5%, 2nd stage mHBA 5.0%, mHBOH28,
It was 2%.

The amount of liquid flowing out from the second stage cathode tank was 65 g/hour.

m HB OH yield 85.0%, current efficiency 66

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between solution temperature and mHBA decomposition rate after 5 hours in aqueous sulfuric acid solutions of mHBA at various concentrations. FIG. 2 is a solubility curve of m HB A at various temperatures in aqueous solutions of various concentrations added with mHBOH DI+. Patent source Mitsui Toatsu Chemical Co., Ltd. 1m

Claims (1)

[Scope of Claims] 1) When m-hydroxybenzoic acid is electrolytically reduced with an acidic aqueous solution, m-hydroxybenzyl alcohol is present in the electrolytic solution while continuously adding m-hydroxybenzoic acid as a raw material and the acidic aqueous solution. 1. A method for continuous production of m-hydroxybenzyl alcohol, characterized in that electrolysis is carried out at 20 to 70°C. 2) Claim No. 2, wherein the reaction temperature is 30 to 60°C
The method described in section 1). 3) The method according to claim (1), wherein the acidic aqueous solution is a 10-20% by weight sulfuric acid aqueous solution. 4) The method according to claim (1), in which continuous electrolysis is performed in a multistage electrolytic cell.